When an aircraft flights under icing conditions, ice accretion very probably occurs at positions such as front edges of the wing and the cow of engine inlet. Icing results in the degradation of stability and operation of the aircraft, loss of aerodynamic performance and reduction of flight safety margin.
Most civil aircraft are equipped with the flight ice detection which can provide ice alert information for pilots to activate anti-ice system or auto-activate ant-ice system. The ice detection system is an important improvement for flight safety.
U.S. Pat. No. 4,553,137 discloses an ice detector based on a vibrating principle of magnetostrictive material. A probe of the ice detector is made of magnetostrictive material. When the aircraft enters icing conditions, increase of mass due to the ice causes the probe's vibration frequency to fall, and an icing signal is sent after the vibration frequency falls to a threshold value. This type of ice detector is extensively applied to aircraft such as A340, A380, B747, B777, ERJ-190, CRJ200 and ARJ. U.S. Pat. No. 7,104,502 also discloses an ice detector based on a vibrating principle of magnetostrictive material, which can improve ice detection performance at near freezing conditions by changing the supporting shape of the ice detector in U.S. Pat. No. 4,553,137.
U.S. Pat. No. 7,370,525 discloses a photoelectrical ice detector. U.S. Pat. No. 4,461,178 discloses an ultrasonic wave ice detector. U.S. Pat. No. 5,748,091 discloses a fiber optic ice detector.
In the paper Icing Detection Using Image-based 3D Shape Recovery (see Computer-Aided Design and Applications, 7(3), 2010, pages 335-347) published by Chunsheng Yu and Qingjin Peng, two sets of cameras are used to obtain icing pictures of power transmission lines, and an ice shape is obtained by image 3D reconstructing and contrast to judge whether ice is formed on the power transmission line; in Ice detection using image analysis (see http://winterwind.se/2012/download16_Combitech.pdf) published by COMBITECH Corporation of the United States is described a technology of using a camera to obtain a blade icing picture and analyzing and monitoring ice on blades of a wind power generator based on the images. Then, image processing technology is introduced into the field of icing detection. However, this kind of device is large in size and heavy in weight and inappropriate to be mounted on an aircraft as a flight ice detection.
Under near freezing conditions, there is a critical temperature difference between the ice detector and the edge of waiting/nacelle (the critical temperature of ice detector is higher than that of the front edge of wing/nacelle). The critical temperature difference can result in the ice accretion on the edge of wing/nacelle prior to the ice detector.